1. Field of the Invention
The present invention relates to novel polymeric compositions of matter comprising a semirigid copolyamide and at least one suitable elastomer having excellent flexibility and resilience characteristics, especially at low temperatures. The present invention also relates to processes for the formulation of the subject polymeric compositions, to means adopted for carrying out same and to shaped articles prepared therefrom.
2. Description of the Prior Art
The polyamides have long been known to this art for their excellent mechanical properties, very good heat resistance and abrasion resistance and also excellent surface appearance. Molded or extruded polyamides have found numerous applications in appliances and machinery for domestic or industrial use, in the electronics industry, in automotive components, in gear wheels, etc. There are, however, certain particular applications in which there is a need for polyamides having greater flexibility than that of the conventional polyamides such as nylon 6,6 (a polymer of hexamethylenediamine and of adipic acid) or nylon 6 (a polymer of .epsilon.-caprolactam); as exemplary of fields of application where this need exists, representative are the manufacture of shoe soles, of tightening bands used in the electrical industry, of internal packings and of flexible hoses used in the automotive industry. Polyamides which are suitable for these applications are known and described, for example, in French Patent No. 2,407,227 and in French Patent Application No. 79/17,264 published under No. 2,459,810. The polyamides according to the aforementioned French patent are prepared by employing a mixture comprising a salt of a particular fatty acid dimer and hexamethylenediamine, and caprolactam, the said salt being in the form of a solution in a particular solvent based on a mixture of water and an alcohol having fewer than 5 carbon atoms, a mixture of water and caprolactam or caprolactam itself. The dimeric acids employed are obtained by polymerization of mixtures comprising a major proportion of monomeric fatty acids having from 16 to 20 carbon atoms and a minor proportion of monomeric fatty acids having from 8 to 15 and/or from 21 to 24 carbon atoms. Moreover, the process of preparation is carried out in such manner that the stoichiometry of the salt is rigorously adhered to by measuring the pH of the salt in solution in a well-defined solvent medium which is not necessarily the same as that used in the preparation of the reaction mixture. The polyamides according to the aforementioned French patent application are prepared from fatty acid dimers of the same type as described above, adipic acid and hexamethylenediamine, while ensuring that the molar ratio of adipic acid to total acids ranges from 0.5 to 0.99 and employing a series of operations under conditions of temperature and pressure which are selected such as to provide homogeneous copolymers which exhibit only a single phase in the molten state or in the solid state.
Nonetheless, experiments which have been carried out with semirigid copolyamides according to the above-mentioned patent or patent application indicate that their flexibility (measured in the usual manner in terms of the value of the flexural modulus and torsional modulus) and their impact strength, which are at a satisfactory level at ambient temperature, on the other hand decrease greatly when the molded articles shaped therefrom are subjected to low temperatures such as those ranging from 0.degree. C. to -40.degree. C. This is a disadvantage which considerably restricts the entry of these semirigid polyamide articles into certain markets, such as the sports and leisure markets.
It too is known to incorporate plasticizers into polyamides in order to increase their flexibility and resilience. However, this method does not provide satisfactory results. In fact, the majority of the plasticizers suitable for plastics are insufficiently compatible with polyamides and separate out partially, through migration, during processing; moreover, these plasticizers, which are able to lower the flexural modulus and torsional modulus at ambient temperature and to increase the impact strength are on the other hand generally ineffective and even detrimental in respect to resilience properties at temperatures below 0.degree. C.